Jerome is a brave, determined and serious dog.He faces hardships with a calm attitude. Jerome is very attentive and often notices things the other dogs don't.

Jerome the responsibility of his actions. He was very devoted for his job and seems like he was slightly brainwashed by the training, as he believed the dogs have to bear any kind of treatment from humans without fighting back. It's been mentioned that his past as a contract killer has scarred his mind.

He was ready to sacrifice himself and his minions for their mission.He greatly respects Gin, Smith, and Weed who are all ready to sacrifice themselves for others. From them, he learned to sacrifice himself for his friends. He was also deeply moved when Weed and his friends were ready to sacrifice themselves for him.

He especially respects Weed and wants to protect him no matter what, believing that Weed has the unique sense of justice the world needs. Weed's great sense of justice made Jerome see his own morals as ugly and unclean. He seeks to become more like Weed in sense of moral.

Jerome knows he isn't fully good-hearted and believes there is some evil inside him. According to him, he doesn't seek for happiness and isn't good-hearted enough to live for the happiness of others.He was ready to disobey Weed's order and kill the Hōgen's spies in order to protect his comrades and also in order to do the dirty work for Weed.

He isn't afraid of death but he seems to be very afraid of humiliation. He feels great shame because he ordered his minions to die and didn't die with them. He believes he has no right to lead anyone and that only his death will be amend for the deaths of his minions. He constantly seeks for a place where he can die a honorable death, often doing rather suicidal actions and wishing to die instead of living in constant shame.

He is very afraid that instead of a honorable death, he will die a shameful one. Once Hōgen almost managed to fulfill this fear.

Jerome is a trained guard dog and assassin. He was sent after P4 by his creators to destroy it. He originally had 13 subordinates; the last four of them (Rocca, North, Robert, and Wheeler) were killed by P4. After the death of P4 and all was peaceful once more, he became Weed's adviser, and taught him how to fight better.

When a human shot his leg with a bullet, the Kōga ninja dog Tesshin offered to take it out one night, but Jerome told Tesshin to keep the bullet in his leg as a punishment for his previous actions as an assassin.

Later, Jerome was driven out of Weed's pack by Weed himself when he murdered two of Hōgen's assassins: Lector and Thunder. He worked for Weed independently from then on, along with his new pack of Shikoku dogs. Jerome finally meets Weed after saving Reika from a river. He then saves GB from Hōgen. As he fought Hōgen, pain struck into his leg due to the bullet.

Jerome is then thrashed by Hōgen and is thrown into the river. Weed jumps in and tries to save Jerome. In the river before his death, Jerome had saved Weed by holding his head above the water until he was rescued. Jerome eagerly awaits to meet his fallen comrades again and, interestingly, P4 too. In the last episode, Jerome's ghost appears to Weed in a field of flowers, but then vanishes.

Some fans are still in doubt if he really died in the anime or if he survived and he actually apeared to Weed but left.

Jerome was one of the guard dogs who's job was to make sure that P4 didn’t escape from the scientific institute. When P4 escapes anyway, Jerome and his soldiers do everything they can to stop him. Jerome meets Weed in the mountains of Ōu where he at once realizes that he is the son of Gin. He now tries to get Weed to join the fight against P4 and succeed. During the fight, P4 kills all of Jerome’s soldiers and hurts Jerome badly.

However, P4 dies and Jerome survives. He then joins Weed’s group to find and help Weed’s father, Gin, the Great Leader of Ōu. Jerome gets shot in the leg by a human and has to fight one of the humans’ dogs called Ron. Ron bites off Jerome’s ear but looses the fight.

Jerome is known in the pack as the assassin, a name which he lives up to. When he discovers two of Hōgen's spies, he kills them even though Weed told him to leave them alone. As a punishment, Weed sends him away from his pack. However, Jerome does not leave Weed entirely, but stays close in case something should happen. He is welcomed back when the fight against Hōgen begins.

Jerome and Weed are the first to feel Hōgen's fangs and they are thrown into a roaring river. Here, Jerome nearly kills himself when trying to keep Weed's head above the water. Because of this, Jerome cannot participate in the final battle, but is brought to the human, Daisuke, by GB.

Just as Hōgen is defeated, Jerome hears the howls of the Ōu army whilst in the care of Daisuke. Once he is fully recovered, he is relased back into the wild. Jerome travels up to the mountains and is ambushed by monkeys who are after some puppies. Here, he encounters Yukimura, Weed's older brother, who saves him from the monkeys. When Weed comes to search for Jerome, he too meets Yukimura. All of them join forces to kill the baboon general, Shōgun, who threatens to take over Yukimura's territory.

Lydia and Jerome

Again, Jerome manages to escape Weed and flee to Hokkaidō where he hides in shame over his past (By this it meant the episode where he killed Hōgen's spies). In Hokkaidō, he meets Hakurō, an old Ōu warrior.

Hakurō tells Jerome to watch out, since intruders have started to threaten their land. Jerome doesn't listen very carefully and is soon face to face with one of the intruders, a female German Shepherd named Lydia.

Lydia lures him into an ambush where the leader of the intruders, a German Shepherd named Victor, attacks him. Jerome is seriously wounded and taken hostage. Lydia tries to trick him into telling where Hakurō is hiding, but Jerome tricks her instead. He fakes the seriousness of his wounds and Lydia believes that there's no need to guard him. Jerome escapes as soon as she leaves and flees back to Hakurō, who leaves him to recover at the Collie, Ram's home.

When Jerome is recovered, he runs back to help Hakurō, only to find he was killed by Victor. Unfortunately, he bumps into Victor and is taken hostage again. However, he is not killed since Lydia manages to convince Victor that they need Jerome alive. Slowly, Jerome starts to fancy Lydia and they both fall in love. Victor leaves Jerome behind, guarded by Lydia. Suddenly, the Ōu commander, Akame appears and follows Jerome to the Ōu army's base for safety. Jerome follows Gin's platoon when they are all taken hostage by Victor in a gorge.

In the gorge, Jerome and the others face many days without food or water. When the fight begins between Victor's army and the Ōu army, Jerome takes part in the fight, but is quickly knocked out by Bozlev. When he comes to, he continues to fight alongside Lydia. Like most of the Ōu army, Jerome is badly wounded by the Russian dogs. Shortly, Daisuke and Hidetoshi appear on the scene and Jerome is healed along with the rest of the injured dogs.

After the battle against the Hybrid bears ends, Jerome has 6 pups with Lydia.

Jerome survives the volcanic disaster along with his mate Lydia and their puppies. They remain in the shed with the other dogs until freed where they return to the mountains to look for Weed and other missing members of the group.

Jerome accompanies Weed to investigate the strange scent in the air. As Weed checks on a body of a dog killed by Monsoon, Jerome notices the giant bear behind him and tries to help, but is too late when Weed is fatally injured. Jerome helps the unconscious Weed onto Ken's back to take him safety, unaware that his wife and children have also been attacked and fatally injured by other bears. Upon returning to Gin after hearing his howls, Jerome finds three of his children dead and his mate fatally wounded, whilst comforting her, she dies from her wounds. Jerome hugs her body and cries. He then attempts to make a suicide attack but is stopped when everyone reminds him of his surviving children, to which he breaks down and cries.

Jerome calms down and goes back up the hill with the pups. Gin suggests that while the others get away, he acts as a decoy but is told by Jerome and Kurotora not to do it and they will do it instead. Gin doesn't listen and charges at Monsoon, but his Battōga does nothing and Gin is easily thrown off. In a state of panic and anger, the dogs charge at the bears themselves. Monsoon easily slashes at them all, killing Jaguar and badly injuring Jerome and the rest.

Jerome manages to get up from his injuries and fight the bears attacking his family. He asks Sunny and Maru to put Lydia on his back to take her away for a later burial. As he runs off with her, a strange Doberman runs straight into him, claiming if he lets Jerome go, his life will be at stake.

In a fit of rage, Jerome attacks the bears again, and strikes Monsoon's ankle. In defense, Monsoon lifts his foot up and slams it back on the ground, crushing Jerome beneath it. Musashi comes to his aid but is impaled on Monsoon's claws.

Monsoon lifts up his leg to carry out his attack on the rest of the army, leaving Jerome badly injured on the floor. After this defeat, Jerome is carried to a makeshift prison made my Monsoon.

As the bears grow hungry, they decide to feast upon the dogs and open a small hole in the prison to reach inside. Jerome along with Hook and Izō stay back from the claws as the bear tries to grab them. In a bid to stop the bear, Jerome bites one of the bears fingers, tearing the claw out from its socket and forcing the bear to retract its paw in pain.

Days later, Jerome is surprised to see Mole digging his way into the prison. With the help of Gennai's follower and Mole's children, Jerome and the others are one by one taken out the prison. Despite his injuries, Jerome goes to Daisuke's house to meet with Cross and his two children. He scolds his son, Maru, lightly, asking him how long he plans to hide under the house when he should be fighting for the others. Sunny and Maru head off to join the fight, but Cross stops them. Jerome collapses from his wounds and as his children find the Ōu army, Jerome stays with Cross. Jerome discourages her from doing so, as his children need to show their gratitude to the Ōu army by helping them fight.

Jerome lies under Daisuke' s house but is noticed by Daisuke and brought to Hidetoshi for treatment. Inside, George is being tended to and Gin is in his vet cage. Jerome quickly greets him.

"The world can not laze any time."- Jerome refusing to rest, for the hunt against MonsterGinga Densetsu Weed, volume 4

"I don't seek a happy life. And I'm not so good-hearted that I would live for the happiness of others!"- Jerome thoughts of death by choice Ginga Densetsu Weed, volume 14

"Live for something! Nobody is born into the world in vain."- Jerome speaking with RonGinga Densetsu Weed, volume 15

"All dogs can live in peace. I'm telling you that, because you do not know it. There is a paradise for dogs on the island next to this one. The races do not oppress another, but we all live in one group, helping each other."- Jerome talking about Ōu to LydiaGinga Densetsu Weed, volume 39

"My flesh is mortal, but my mind will not be break!- Jerome to the Russian Army Ginga Densetsu Weed, volume 39